Thermochemics and kinetics of the hot dip galvanizing reaction by electrochemical method.

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Thermochemical properties of liquid Zn-Al-Fe ternary alloys equilibrated with so-called dross phases, which are solid Fe-Zn and Fe-Al intermetallic compounds, have been made by an emf method using Al concentration cell composed of composite mixed chloride and sodium beta-alumina solid electrolytes.The construction of the cell can be expressed as follows.JA01HYThe emf of the cell is written by the following Nernst's equation.JA02SUThe chemical potential of Al in the alloys has been obtained as a function of temperature from the emf measurements, and the potential diagram has been constructed to illustrate the stability domain of the intermetallic compounds in equilibrium with liquid phses as functions of Al potential and temperature.The present results indicate that the delta+Fe_2Al_5+liq. threephase region, which corresponds to the boundary of the stability domain of delta_1 and Fe_2Al_5, branches into GAMMA_1+Fe_2Al_5+liq. regions at 460ﾟC,suggesting that GAMMA_1 phase becomes stable … More below this temperature. The GAMMA_1 phase showed marked grain growth and the solubility of Al was found to be higher than thatin delta_1 phase. From the comparison of metallographic observation of both GAMMA_1 and delta_1, the present author suggest the mechanism of transformation and growth of GAMMA_1 phase from delta_1 phase. The present observation that the GAMMA_1 phase can coexist with liquid phase was also confirmedby the results that the bottom dross sampled at CGL pot was the single phase of GAMMA_1. Also suggested by the inflection of emt-temperature relationship was the possible existence of the higher order transition in delta_1 phase, which is termed as delta'_1 phase, and the stability domain of delta'_1phase is illustrated in the potential stability diagram. Details of the structural information of this phase, however, is not fully established at this moment. Further discussion has been made based on the compositional analysis of the dross sample by illustrating the isothermal section of the ternary composition phase diagram with the comparison with the previous reports. Based on both potential stability diagram and the composition diagram, experimental results for simultaneous measurement of spatial distribution of both temperature and Al potential in the CGL pot has been analyzed, and the formation mechanism of GAMMA_1 phase in the pot hasbeen discussed in conjunction with the surface damage by the grain-grown dross particles suspended in the molten zine in the pot. Less